Methods of manufacturing high performance insulations

ABSTRACT

A durable, low-density, high performance insulating material is suitable for use as a high temperature thermal and acoustic insulation. The insulation includes fiber batting made with non-thermoplastic fibers or blends of fibers such as aramid fibers and ceramic fibers, which are bound within at least some interstices by high temperature non-flammable thermoplastic binder such as polyphenylene sulfide. In addition, a fireblocking layer can be provided on at least one surface of the insulation to further improve fire ablation or flame retardance.

This application is a divisional of application Ser. No. 09/369,557,filed Aug. 6, 1999, now U.S. Pat. No. 6,383,623.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to high performance materials having superiorthermal and/or acoustic insulative properties. More particularly, thisinvention relates to low-density thermal and acoustic insulation whichcan withstand elevated temperatures while retaining its insulativeproperties. In addition, this invention concerns insulation materialsuitable for use in aviation. Other aspects of the invention involvemethods for manufacturing such insulation.

A modern airplane has a layer of insulation located just inside theplane's exterior skin for the purpose of limiting the flow of heat intoand out of the plane's cabin. Since the temperature at the cruisingaltitude of commercial jets may be −30°, while the temperature in thecabin is approximately 70°, the resulting 100° temperature gradientwould, unless thermal insulation is used, lead to a significant loss ofheat from the cabin.

Insulation also serves to reduce the noise level in the cabin, suchnoise being produced both by the plane's engine(s) and the plane'smotion through the air.

Typically, the insulation used in planes is composed of singular ormultiple layers of finely spun fiberglass blankets of various densitiesdesigned for thermal and acoustic protection, the latter against bothhigh frequency sounds from jet engine noise as well as structural-bornelower frequency sounds. This material is very fine in fiber diameter andtends to fracture easily.

Conventional aircraft insulation has a number of shortcomings. Ashighlighted by several recent incidents involving the suspected failureof aircraft insulation, the most problematic of these shortcomings isthe material's performance in fires. At elevated temperatures, which maytypically approach 2000° F., conventional aircraft interior materials,including insulation, because of the materials from which it is made,begins emitting substantial quantities of thick, toxic smoke. Carbonmonoxide and hydrogen cyanide are the two principal toxic combustiongases. Most cabin furnishings contain carbon and will generate bothcarbon monoxide and carbon dioxide when burned. Burning wool, silk andmany nitrogen-containing synthetics will produce the more toxic hydrogencyanide gas. Irritant gases such as hydrogen chloride and acrolein, aregenerated from burning wire insulation and some other cabin materials.Generally, carbon dioxide levels increase and oxygen concentrationsdecrease during fires. Although fire is a great danger, it has beendetermined that the toxic smoke produced by the smoldering insulationand interior materials is a grave threat in its own right. The blindingsmoke will interfere with the evacuating passengers' finding the plane'semergency exits, and because it is toxic, it may asphyxiate passengerswho do not escape quickly. More people could be killed throughasphyxiation by toxic smoke than might die in the fire itself.

Recent incidents involving the suspected failure of aircraft insulationconfirm the need for safer, more thermally-stable insulation. In Octoberof 1998, the Federal Aviation Administration (FAA), responding to thecrash of a Swissair flight near Halifax, Nova Scotia, a month earlier,recommended the replacement of the insulation in nearly all of theworld's 12,000 passenger jet planes. The FAA has also warned that theMylar insulation used in passenger planes can catch fire when exposed toelectrical shorts, and so the FAA has established new flammabilitystandards for airplane insulation that require materials to withstandhigher temperatures for extended periods of time.

One approach to improving aircraft insulation's performance is toprovide the insulation with a protective outer layer. The FAA hasinvestigated “hardening” aircraft fuselages to increase the time ittakes flames outside an aircraft to burn through the plane's fuselage.One “hardening” technique under investigation involves usingheat-stabilized, oxidized polyacrylonitrile fiber (PAN), which maydouble the time it takes flames to penetrate into the plane's cabin.Barrier materials, such as those utilizing PAN, are composed of a randomfiber mat or felt used in conjunction with existing fiberglass systemsfor improved fuselage burnthrough times.

Incidentally, this “hardening” approach is similar to that described inU.S. Pat. No. 5,578,368. The '368 patent describes a material for use insleeping bags having a protective outer layer made from aramid fiber,and the patent says this aramid layer imparts fire-resistance.

Accordingly, there is a real need for aircraft insulation which is ableto sustain high temperatures without burning, smoking, degrading oroutgassing. It is also desirable that when such insulation finallyburns, it does so in a self-extinguishing manner.

“Low-performance” insulation commonly used in building construction forwall and ceiling barriers, as well as pipe wrappings, and even inaerospace applications such as aircraft thermal blankets, is typicallymade from a lightweight batting of glass fibers held together by athermoset phenolic resin binder. This insulation material, commonlyreferred to as “fiberglass insulation”, is inexpensive and may besuitable as a low temperature thermal insulator and sound absorbingmaterial. Such insulation has a number of serious shortcomings.

For example, fiberglass insulation is brittle in nature, meaning thatwhen it is handled, airborne glass particles are produced. Those workingwith the fiberglass insulation may inhale the airborne glass particles,irritating their lungs. Glass particles may lodge in the workers' skin,also causing irritation. Although those handling the fiberglassinsulation can protect themselves by using respiratory masks and wearingprotective gear, that results in added expense and inconvenience.

Another shortcoming of fiberglass insulation is that the material ishydrophilic, meaning water can permeate into and be absorbed by theinsulation. The absorbed water decreases the insulation's thermal andacoustic properties, and also increases the insulation's weight, whichis a serious problem if the insulation is used in aviation. Sinceairplane insulation is mounted against the plane's skin, the insulationbecomes quite cold when the plane is in flight. When warm, moist air,such as the air in the cabin, passes over the insulation, the water inthat air condenses on and collects in the cold insulation. Over time,the insulation may become soggy, reducing its insulating abilities, andheavy, increasing the plane's operating costs. While it may be possibleto reduce water absorption by treating the fiberglass insulation orproviding a barrier layer, this complicates the manufacturing processand makes the insulation more expensive.

Accordingly, there is a need for alternative insulative materials whichhave superior thermal and acoustic properties, without the inherentdisadvantages of conventional insulation.

2. Description of the Related Art

It is generally known to provide composite materials, typically,textiles or filtration members, in which non-thermoplastic materials,for example, aramid fibers, are combined with thermoplastic materials,for example, polyphenylene fibers. A variety of such composite materialsare discussed in U.S. Pat. Nos. 4,502,364, 4,840,838, 5,049,435,5,160,485, 5,194,322, 5,316,834, 5,433,998, 5,529,826, and 5,753,001.

Blending of non-thermoplastic fibers with thermoplastic fibers to formconsolidated composite materials is discussed in U.S. Pat. Nos.4,195,112 and 4,780,59. The structures described in these patents aremeant to serve as high density composite materials, and are intended tobe used as load bearing and structural panels or as shape retainingmoldable forms. It is important in considering these compositions tonote that the disclosed structures are quite dense and fullyconsolidated, with nearly fiber-to-fiber contact and high shear loading.These structures have nearly saturated fiber to resin matrix interfaces,contributing to the high strength of these materials.

The binding of fiber blends may employ the use of low temperature sheathcore technology. Such binder fibers are known as bicomponent fibers.Bicomponent fiber technology is discussed in U.S. Pat. Nos. 4,732,809and 5,372,885. Bicomponent staple fibers have a low melting temperaturesheath surrounding a higher melting temperature core, and are designedto sinter adjacent fibers upon softening, as disclosed in U.S. Pat. Nos.4,129,675 and 5,607,531. The '531 patent notes that the materials to becoated include aramid or polyphenylene sulfide fibers, and that coatingmaterials which can be applied include polyphenylene sulfide.

Binding of fibers may also be accomplished using powder or pelletsdispersed into a fibrous web to bind adjacent fibers. Powders may beapplied through the use of carrier emulsions as well as spray or staticcharges to adhere the powder to the matrix fibers. Processing materialsto achieve an even distribution of thermoplastic powder within the webis difficult and does not permit sufficient consolidation of meltedmaterial around adjacent fibers to serve as a structural node orjunction. The use of powders as a binder in fibrous webs is discussed inU.S. Pat. Nos. 4,745,024 and 5,006,483.

SUMMARY OF THE INVENTION

Having recognized the need for high-performance insulation, the inventorhas conducted a detailed investigation into the fabrication ofinsulation components, and insulation constructions which provideimproved fuselage burnthrough performance.

Based upon this investigation, materials have been developed which offersuperior thermal and acoustic performance that matches the currentmaterial's light weight, yet does not shed airborne fibrous particleslike fiberglass insulation. Furthermore, such material is inherentlyfire retardant, and the thermal and acoustic properties of the materialcan be tailored to specific applications by varying the diameter anddensity of the fibers used therein.

More specifically, the present invention employs high-performancecomponent materials which are, because of their fire retardancy and lowtoxicity, particularly suited for use in aerospace insulationapplications. The combination of such high performance materials in thecurrent invention has produced insulation possessing unexpected thermalacoustic and physical properties not available in conventionalinsulating materials.

In addition to being well-suited for aerospace applications, thisinvention can also be used as fire retardant building insulation, hightemperature insulation for pipe wrapping, fireman's turnout gear,padding material, high temperature gasketing or filter media.

In contrast to known bicomponent binder fibers, powder binders andcomposite materials, the present invention relies on melting of athermoplastic material to encapsulate adjacent non-thermoplastic fibers.The encapsulated fibers create strong structural junctions responsiblefor the materials' exceptional resiliency. Also the functional maximumtemperature of known bicomponent fibers does not extend to the hightemperatures at which the present invention can be used.

It is accordingly an object of the present invention to provide amaterial that is well-suited for advanced aerospace and high temperatureinsulating applications, especially for use in thermal and acousticblankets for commercial aircraft.

A further object of the present invention is to provide an insulatingmaterial incorporating a fireblocking materials within the body or as anablative layer which addresses the FAA's desire for the development ofimproved fuselage burnthrough materials for commercial aircraft.

A further object of this invention is to provide an insulating materialhaving a mass of fibers, which fibers include a non-thermoplasticmaterial; and nodes of thermoplastic material. The nodes at leastpartially surround and link portions of at least some of the adjoiningfibers.

Another aspect of this invention concerns a method of manufacturinginsulating material. This is accomplished by providing fibers ofnon-thermoplastic material, providing a thermoplastic material, andmixing the non-thermoplastic and thermoplastic materials together toobtain a fiber mix. The fiber mix is heated so that at least some of thethermoplastic material melts and forms globules which at least partiallyenclose portions of the non-thermoplastic fibers, and then the fiber mixis cooled so that the melted thermoplastic material globules form nodesthat hold the non-thermoplastic fibers together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an unheated homogeneous blend of m-aramid and polyphenylenesulfide fibers which are then processed in accordance with the presentinvention.

FIG. 2 depicts the homogenous blend of fibers from FIG. 1 followingheating.

FIG. 3 compares the airflow resistance for insulation prepared inaccordance with this invention to the airflow resistance of varioustypes of conventional insulation.

FIG. 4 compares the acoustic performance of insulation according to thepresent invention to that of various types of conventional insulation.

FIG. 5 compares the acoustic performance of insulation according to thepresent invention to that of insulation composed of smaller diameterfibers and greater pack density.

FIG. 6 compares the thermal conductivity of the present invention andother types of insulation.

FIG. 7 is a photograph, taken through an optical microscope, ofinsulation according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides high-performance fibrous insulationmaterials that can survive exposure to high temperatures. Such materialsare resilient even under repeated application of line and pointloadings. Such high-performance insulation possesses thermal andacoustic insulative properties superior to conventional insulatingmaterials.

The inventor has discovered that high-performance insulation can beobtained by processing a mass of fibers that includes fibers ofnon-thermoplastic material so that points where fibers touch or at leastapproach one another (hereafter called “contact points”) are at leastpartially enclosed by a binder material. As shown in FIG. 2, the bindermaterial which encloses the contact points of the non-thermoplasticfibers 1 forms a node of material 3 at each such contact point. The nodeof material is, as will be discussed in greater detail hereafter,preferably made of thermoplastic material having a high meltingtemperature.

Insulation materials in accordance with this invention can bemanufactured as follows.

Batting having a blend of non-thermoplastic fibers and thermoplasticmaterial (fibers or otherwise) is provided. Suitable non-thermoplasticfibers include meta-aramid, para-aramid, melamine, PAN, polyimide,polybenzimidazole and polyphenylenebenzobizoxazole. Suitablethermoplastic fibers include aromatic polyketones (PEEK, PEKK), liquidcrystal polymers, polyphenylene sulfide (sulfar), and thermoplasticpolyimides (PAI and PEI). The batting, containing both thenon-thermoplastic fibers and the thermoplastic material, is heated to atleast the melting point of the thermoplastic component such that whileliquid, the thermoplastic material coalesces to form globules at leastin part at the contact points of the non-thermoplastic fibers. Ifhigh-performance thermoplastic materials are used, the minimumtemperature to which the batting should be heated is approximately 538°F., which is roughly the minimum temperature at which suchhigh-performance materials melt. The non-thermoplastic fibers do notliquify because they oxidize, rather than melt, at a temperature wellabove that to which the batting is heated. The batting is then allowedto cool, and the thermoplastic material solidifies.

It will be appreciated that the degree to which the contact points ofthe non-thermoplastic fibers are encased in nodes (the cooled globules)of thermoplastic material can be varied, as discussed in detail below.This is important because the degree to which the contact points areencased in thermoplastic material may affect the insulation material'sproperties, meaning that the degree to which the contact points areencased in thermoplastic material can be controlled so that theinsulation material has preferred physical, thermal or acousticproperties. As previously noted, the degree of encasement by thethermoplastic material can be controlled according to the amount ofthermoplastic material present in the blend. To increase the amount ofthermoplastic material, either a greater amount of a given diameterfiber could be provided, or fiber of a larger diameter could be used. Inaddition, the temperature to which the blend is heated, and the timethat it is held above the thermoplastic material's melting point, can becontrolled to regulate the degree of encasement. The greater theopportunity the thermoplastic material has to melt and coalesce, themore of it will collect at the contact points of the non-thermoplasticmaterial. Thus, holding the blend at a high temperature for asubstantial period of time should result in insulation with more nodesthan material formed by holding the blend at a lower temperature forless time.

Achieving sufficient temperature to melt the thermoplastic binder fibersmay be accomplished using any number of methods for heating a fibrousweb, including radiant heat, a conventional oven, steam or microwaves.

FIG. 7 is a photograph of a sample of insulation prepared in accordancewith this invention. In a fashion similar to that shown in FIG. 2,m-aramid fibers 1 are held to one another by nodes of thermoplasticmaterial 3.

It is important to note that the thermoplastic material does not merelysoften, but it actually melts. The liquified thermoplastic material,presumably under the influence of surface tension, collects and whencooled forms nodes where the non-thermoplastic fibers come together.

A further general example of insulation according to this invention canbe made as follows, with reference being made to FIG. 1. Battingcontaining an intimate blend of between approximately 60-90% meta-aramidfibers (m-aramid) 1 and between approximately 10-40% polyphenylenesulfide (PPS) 2 is provided. The fibers contained in the batting aresuch that the fiber forming substance of the meta-aramid fibers is along chain synthetic polyimide of which at least 85% of the amidelinkages are attached directly to two aromatic rings. The polyphenylenesulfide fibers are a long chain synthetic polysulfide that has at least85% of the sulfide linkages attached to two aromatic rings. It should benoted that the fibrous components in FIG. 1 are blended and entangled atentangled areas 3.

The batting containing the m-aramid and PPS fibers is heated to at leastthe melting point of the thermoplastic component so that, while in thehot liquid phase, the PPS fibers melt and collect at the crossing pointswithin the interstices of the non-melted m-aramid fibers. The batting isthereafter cooled. An example of the batting so treated is shown in FIG.2. Here, a lattice structure created through melting of thethermoplastic binder fibers 2 first seen in FIG. 1 can be seen. It isparticularly interesting to note that the thermoplastic PPS fibers 1first seen in FIG. 1 are consolidated around adjacent m-aramid fibers 2,resulting in an interconnected structural network of bound m-aramidfibers 3. It should be understood that the particular temperature towhich the blend is heated should be chosen in consideration of thematerials used in the blend. In the case where m-aramid and PPS fibersare employed, the blend could be heated to within a range exceeding 538°F. but not exceeding 575° F. Soaking time at that temperature willdepend on the thickness of the material, although generally 10 minutesof soaking time for each inch of thickness is sufficient to completelymelt thermoplastic binder fibers.

This heat treatment results in a strengthened and supported low densitylattice structure of m-aramid fibers and PPS resin. The melted andsubsequently solidified PPS resin acts as a binder, creating anextremely resilient, low-density material having high thermal resistantproperties. The low-density, high-loft m-aramid/PPS material also hasconsiderable promise for use as acoustic material, and so can serve asan absorber, damper or isolator.

Insulation prepared according to this invention can have a densitybetween approximately 0.1-3.0 lbs/ft³, and more preferably,approximately 0.5-0.6 lbs/ft³.

This invention also contemplates the use of different diameter fibers toobtain insulation having particular acoustic and/or thermal insulatingproperties. For example, insulation could be fabricated with more thanone fibrous layer, and at least some of those layers could havedifferent densities. Different layers also might contain differentdiameter non-thermoplastic fibers. Such differences in layer densitiesand fiber diameters will have an influence on the acoustic and thermalproperties of the material.

It should be kept in mind that the insulation's ability to withstandhigh-temperature service, along with other properties such asflammability, will be affected by the materials which make up both thenon-thermoplastic and thermoplastic fibers. If the insulation is to beused at extremely high flame temperatures (>2000° F.), highlyfire-retardant materials are preferred. A wide variety of known hightemperature materials could be used in combination with the fireretardant fibers that comprise the insulation (fire retardant fiberscomprising the insulation may include meta-aramid, para-aramid,melamine, PAN, polyimide, polybenzimidazole andpolyphenylenebenzobizoxazole) to block or protect these fibers whichoxidize at lower temperatures. Such materials include ceramics,intumescent foams, foils, dense layers of polyacrylonitrile fibers (PAN)or polymer films. Likewise, materials which could be used as thethermoplastic fibers include polyphenylene sulfide (Sulfar), aromaticpolyketones (PEEK, PEKK), liquid crystal polymers and thermoplasticpolyimides (PAI and PEI).

It also will be appreciated that the non-thermoplastic fibers could beeither a single material or a mixture of different materials. So too,the thermoplastic material could be a blend of different substances. Forexample, the blending of two different thermoplastic fibers may be usedto impart desired physical properties whereby each thermoplastic may beresistant to certain chemicals, thus giving the finished material abetter overall resistance to a wider variety of chemicals.

Examples of different insulation compositions proposed in accordancewith this invention will now be discussed.

EXAMPLE 1

An intimate blend of 20% 0.9 denier 1.5″ staple length PPS fibers and80% 2.0 denier 3.0″ staple length m-aramid fibers is formed into a thicklofty batting.

EXAMPLE 2

An intimate blend of 20% 0.9 denier 1.5″ staple length PPS fibers and80% 2.0 denier 3.0″ staple length p-aramid fibers is formed into a thicklofty batting.

EXAMPLE 3

An intimate blend of 20% 1.2 denier 2.0″ staple length PPS fibers and80% 2.0 denier 3.0″ staple length melamine fibers is formed into a thicklofty batting.

EXAMPLE 4

An intimate blend of 20% 1.5 denier 2.0″ staple lengthpolyetheretherketone (PEEK) fibers and 80% 2.0 denier 3.0″ staple lengthm-aramid fibers is formed into a thick lofty batting.

EXAMPLE 5

An intimate blend of 20% 1.2 denier 2.0″ staple length PPS fibers and40% 2.0 denier 3.0″ staple length melamine fibers and 40% 2.0 denier3.0″ staple length m-aramid fibers is formed into a thick lofty batting.

EXAMPLE 6

An intimate bled of 25% 1.2 denier 2.0″ staple length PPS fibers and 80%2.0 denier 3.0″ staple length m-aramid fibers formed into a thick loftybatting with a fire blocking layer comprised of polyacrylonitrile (PAN),ceramic, foil or polymer film, physically attached to at least one sideof the outer surface.

Examples 1-4 were actually prepared, but were not tested. Example 5 is aconceptual example that was not prepared. Example 6 was prepared andtested.

The following insulation was prepared and found to have particularlydesirable properties.

EXAMPLE 7

An intimate blend of 20% 1.2 denier 1.5″ staple length PPS fibers and80% 2.0 denier 3.0″ staple length m-aramid fibers was formed into athick lofty batting.

EXAMPLE 8

An intimate blend of 20% 1.2 denier 2.0″ staple length PPS fibers and40% 2.0 denier 3.0″ staple length m-aramid fibers and 40% 2.0 denier3.0″ staple length PAN fibers was formed into a thick lofty batting.

Material produced in accordance with Example 8, described above, wastested by the Aircraft Fire Safety testing lab of the FederalAeronautics Administration (FAA) technical center in Atlantic City,N.J., and was found to have superior fuselage burnthrough performancecompared to current thermal and acoustic insulating materials used inaircraft. The test was performed using a standard method employed toassess materials for fuselage burnthrough protection using a controlledflame. A 20″ by 36″ by 3″ thick specimen of the material passed a testwhich exposed the sample to a flame temperature exceeding 2000° F. for aminimum of 240 seconds.

Material Performance

Samples of low-density, high-loft insulation prepared in accordance withthis invention were tested for thermal and acoustic properties. Thesesamples also underwent a standard physical property assessment, whichexamined each sample's thickness, density, tensile strength, resistanceto crushing, elongation and mullen burst strength. The samples testedcorrespond to the configuration of material described in Example 7,above.

Thermal testing was performed in accordance with ASTM C518—Steady StateHeat Flux Measurements and Thermal Transmission Properties, using a HeatFlow Meter Apparatus (testing conducted by Holometrix-Micromet, ofBedford, Mass.). As shown in FIG. 6, which is a graph depicting thecomparative thermal conductivity of different materials, the low-densitym-aramid insulation showed significantly superior insulating propertieswhen compared with conventional insulating materials of similar densityand fiber diameter as well as materials used for aircraft fuselageinsulation applications such as Nomex® needle felt, Johns MansvilleMicrolite AA® blanketing, and Johns Mansville Microlite B® blanketing.

Acoustic testing was performed in accordance with ASTM C522—AirflowResistance and ASTM C423—Sound Absorption and Sound AbsorptionCoefficient by Reverberation Room Method (testing conducted by Geiger &Hamme, L. L. C., Ann Arbor, Mich.). FIGS. 4 and 5 show the acousticperformance of insulation prepared in accordance with this invention.FIG. 4 shows the acoustic performance of the low density m-aramidmaterial described in the current invention compared to the performanceof similar typical fiberglass insulation. FIG. 5 shows the acousticperformance of insulation in accordance with the present inventioncompared with three different samples of conventional types ofinsulation offering similar acoustic performance (represented by ∇, Δand ×); it should be noted that the present invention providesperformance that is at par with or better than conventional materialhaving much smaller diameter fibers. Thus, the present invention offers,on an equivalent basis, superior acoustic performance.

The average noise reduction coefficient (NRC) was measured for eachmaterial and plotted on the right side of the graph. The plot shows thesuperiority of the m-aramid material over fiberglass material of similardensity and fiber diameter. The low density m-aramid materialperformance is superior to similar fiberglass materials over a widerange of frequencies and reflects a significantly better acousticinsulator.

FIG. 3 depicts the relationship between the logarithm of the airflowresistance and the density of insulation material prepared according tothis invention, and shows that this relationship is linear for variousfiber diameters. FIG. 3 also compares the airflow resistivity relativeto density for different materials, including insulation prepared inaccordance with this invention. It should be noted that according toFIG. 3, this invention provides material allowing airflow comparable tothat of a 9-micron diameter glass pack, even though the acousticperformance data for such material, seen in FIG. 5 shows that theinsulation offered acoustic insulation properties equal to that of a 5micron diameter glass pack material. Thus, it will be appreciated thatlow-density high-loft insulation according to this invention offersbetter acoustic properties for a given airflow resistance thanconventional fiberglass insulation.

In FIG. 5, the noise reduction coefficient (NRC) for the 1″-1.0 lb/ft³p-aramid/pps material according to the present invention is 0.70. The 1″thick samples of Owens Corning Aerocor fiberglass insulation havingdensities of 0.7 lb/ft³ and 1.0 lb/ft³ also had NRC's of 0.70. TheAerocor sample having a density of 0.5 lb/ft³ had a somewhat smallerNRC.

The foregoing test data suggests that increasing the insulation'sdensity, while decreasing the fibers' diameters, should improve acousticperformance. Thus, when manufacturing insulation according to thisinvention, one can produce insulation having specific acousticproperties, with adequate airflow to allow for the evaporation oftrapped moisture, by using the appropriate materials to form theinsulation.

Two different samples of insulation according to this invention andconventional fiberglass insulation were compared to illustrate thisinvention's superiority under loads. The samples were placed in a platenpress and loads were applied at levels sufficient to fracture thestructural, or load bearing fibers within the material. Table 1 showsthe results of such testing, and compares both the load applied to eachsample and each sample's subsequent recovery of thickness. It will beappreciated that the low-density high-loft material of this inventionexhibited much greater resistance to crushing than comparable glassfibers.

TABLE 1 Load Recovery (psi) (%) m-aramid/PPS (Trial #1) 406 95m-aramid/PPS (Trial #2) 1306 82 fiberglass batting 312 No Recovery

Table 2 compares the material properties of insulation preparedaccording to the present invention and comparable fiberglass insulation.These tests shown that the insulation of this invention is both moredurable and stronger than the fiberglass insulation. The same testingprocedures were used to evaluate the different samples, and the sampleshaving similar weights, thicknesses, and densities were chosen forevaluation. A direct comparison of the test data shows that the currentinvention is a superior alternative to fiberglass insulation, in partbecause it offers the benefit of durability even after repeatedhandling; loading does not cause the insulation to shed particles. Thisis in contrast to fiberglass insulation, which, as previously noted,undergoes shattering and fragmenting of its component glass fibers whenexposed to loads during installation and maintenance. That is, theinstallation and maintenance of conventional fiberglass insulation ofteninvolves the application of point compressive loads, which fracture andcrush the glass fibers, resulting in the release of glass fragments, anddegrading the material's performance through loss of resilience. Incontrast, insulation according to this invention is unaffected by theapplication of typical point loads during installation and handing.

TABLE 2 test fiberglass m-aramid/PPS method oz/yd² 12.3 13.7 ASTM D3776thickness (in.) 1.0 1.2 ASTM D1777 tensile 2.3 23.6 ASTM D5034 strength(lbs.) Mullen burst 33 485 ASTM D461 strength (psi.)

This invention is meant to encompass the use of a variety ofhigh-performance materials. High-performance materials refer tomaterials having properties which render the resulting insulationsuitable for use in extreme conditions. For example, where theinsulation must be able to withstand use at high temperature, or befire-resistant, a percentage of the non-thermoplastic fibers can beblended with fibers know for use as fire retardant, fireproof and/orablative materials. Examples of such materials include ceramic fibers,melamines, PAN, para-aramid, polybenzimidazole andpolyphenylenebenzobizoxazole. So too, where the insulation is to be usedin chemically aggressive situations, such as highly acidic or basicenvironments, the component non-thermoplastic and thermoplasticmaterials can be chosen to withstand that environment.

The non-thermoplastic fibers used in this invention can range in sizefrom approximately 3-150 microns (0.08-220 denier) with staple lengthsranging from approximately 0.5-15.0 inches (“approximately” means thatsizes outside this range can be used provided they still result in theproduction of material having insulative properties).

The fiber diameter of the thermoplastic material used in this inventioncan range in size from approximately 3-150 microns (0.08-220 denier)with staple lengths of these fibers ranging from approximately 0.5-15.0inches.

The resulting insulating material has a density of approximately 0.1-3.0lbs/ft³.

Insulation prepared in accordance with this invention can be formed intoblocks or rolls suitable for later installation. If desired, theinsulation could in advance of installation be cut to shape; this may behelpful where the insulation is used in a production line such as anaircraft construction line. Material prepared according to thisinvention could also be bonded to structures using heat sealingequipment, latch and hook technology (i.e., Velcro® fasteners) and/orultrasonic welding devices to attach, connect or bond the material toadjacent structures or other like material. This is especially importantin the installation of aircraft insulation where seam failure is anissue in the protection against fuselage burnthrough.

Another embodiment of this invention involves the addition of a fireblocking layer to the insulation. The fire blocking layer may bephysically attached to the insulation by means of mechanical attachment,as in needling, thermal bonding, adhesives or any means which wouldresult in the physical attachment of a fire blocking layer to one orboth sides of the material. This fire blocking layer could be made fromfire retardant or ablative materials such as polyacrylonitrile (PAN)fibers, ceramics, intumescent foams, foils or polymer films.

Alternatively, fireblocking material could be provided within theinsulation itself, for example, by dispersing fireblocking materialthroughout the fiber blend.

Particularly desirable fireblocking results were obtained with a blendof materials composed of approximately 40% m-aramid, 20% PAN, 20% PPSand 20% pre-ceramic fibers. Preferably, such pre-ceramic fibers arefibers of Al₂O₃ (modified silicic acid). The silicic acid materialcontains approximately 95% SiO₂, 4.5% Al₂O₃, and less than 0.2% alkalineoxides, and this material is commercially available as BelCoTex® staplefiber, available from Belchem Fiber Materials GmbH, Germany. Adding thismaterial proved to be extremely effective in protecting adjacent organicfibers and limiting flame propagation. The 20% level is described as anexample that produced desirable results the level of pre-ceramicmaterial used may be more or less depending upon the desired degree ofprotection. The addition of pre-ceramic fibers to the blend, as well asthe addition of an attached layer of ablative or protective barriermaterial to the surface of the insulative material is especiallydesirable when designing material which will offer high temperatureflame protection.

Next, methods for forming various insulation materials in accordancewith this invention will be discussed.

Insulation of the type already described can be manufactured by firstopening and blending fibers, carding and needling the blended fibers,heating the fibers, and then suitably finishing the produce. Each ofthese steps will now be discussed in detail.

Opening and Blending

This invention begins with the selection of a blend of thermoplastic andnon-thermoplastic materials, and the mixing of those materials in anintimate blend. For example, 20% PPS fibers are mixed with 80% m-aramidfibers. The fibers can be blended by an opening process, which entailsthe mechanical agitation and/or mixing of the fibers in a stream of air.During this opening process, blending of the different fibers takesplace, and the fibers become homogeneously mixed.

In a further aspect of this invention, insulation prepared in accordancewith Example 7 could include 20% 2.7 denier, 1.5″ staple length, PPSfibers combined with 80% 5.0 denier 3″ staple length m-aramid fiber, andhereafter will be referred to as Example 9.

Another blend of fibers in accordance with Example 1 (hereafter referredto as Example 10) could be manufactured from a blend of fibers along thefollowing lines: the blend could contain 20% 0.9 denier, 1.5″ staplelength PPS fiber combined with 80% 1.0 denier 3″ staple length m-aramidfiber. This insulation is expected to provide a high loft fabric havingthermal, acoustic and mechanical properties different from insulationmade from the foregoing blend of fibers (Example 9).

Insulation made from the Example 9 blend is expected to be of lighterweight and have less compressive strength than the insulation made fromthe example 10 blend. Also, the insulations made from the blends ofexamples 9 and 10 can be expected to have differing acoustic and thermalproperties.

More specifically, PPS and m-aramid fibers that could be used in thisinvention can range in size from approximately 0.08-220 denier havingapproximately 0.5-15.0 inches in staple length. These fibers could becombined in amounts ranging from between approximately 60-90%non-thermoplastic fibers and between approximately 10-40% thermoplasticfibers. The precise amount of each of the materials used can be chosento provide the finished insulation with desired properties, as can beseen in the two previous examples.

It will be appreciated that the ability to tailor the finishedinsulation material for specific mechanical, acoustic and or thermalapplications through the suitable selection of the non-thermoplastic andthermoplastic fibers combined in the blend provides great flexibilityfor the material designer. This is just one of several opportunitiesthat this invention gives the material designer to control theproperties of the insulation that is produced.

Carding and Needling

The blended fibers are further opened and oriented in a carding process.This process involves forming the staple fibers into a singular web heldtogether by the mechanical interlocking of fibers. Typically, the webutilized in the process weighs between approximately 0.3-15 oz/yd². Aweb weight less than 0.3 oz/yd² proves to be difficult to handle due tothe lack of fiber entanglement, and likewise, a web weight heavier than15 oz/yd² creates a material with a density beyond that of the proposedinvention. For a description of the carding process, see U.S. Pat. No.3,983,273, the contents of which are incorporated by reference herein.

While in the carding machine, the web of fibers is subjected to across-lapping procedure and is then transferred onto a lower apron(floor apron) moving perpendicular to the web of fibers exiting thecarding operation. If desired, multiple layers of the lightweight webcan be laid one atop another by means of a reciprocating apron. If thefloor and reciprocating aprons have different speeds, different numbersof web layers can be produced, enabling the desired batt (multiple webs)weight to be achieved. The batt fiber orientation can be adjusted in thelongitudinal or transverse directions to increase or decrease thein-plane strength properties of the finished material.

The carded web and subsequent layers forming the batting can then beconsolidated through a low-density needling procedure, whichmechanically interlocks the fibers. This low-density needling proceduremay also be utilized as a means of attaching other fibrous layers to thesemi-finished or finished material. For example, a fire blocking orablative layer may be attached to the fibrous batting at this stage inpreparation for further finishing procedures. An example of the needlingprocess can be found in U.S. Pat. No. 3,117,359, the contents of whichare incorporated by reference herein. The needling process uses barbedneedles, which are forced through the material to mechanically entanglethe fibrous layers. This step in the process is accomplished primarilyas a way of allowing the semi-finished material to be handled. This stepof needling may, however, be omitted if in-line curing of the batting isaccomplished.

The inventor has performed this interlocking procedure in connectionwith the present invention using a small pretacking needle loom having adensity of 32 needles per foot, as measured across the width of theboard. The needling procedure was found to increase the density of thebatting from approximately 0.1 lbs/ft³ to approximately 0.5 lbs/ft³.

In this aspect of the invention, two factors are thought to affect thedensity of the final material. The first factor involves the type ofneedle used in the needling operation, and the second factor involvesthe number of web layers which are provided.

It is envisioned that the needles which can be used in this inventioninclude needles of the types commonly employed in the nonwoven textileindustry to produce commercial grade fabrics for use as insulationand/or padding. Examples of such needles can be found in U.S. Pat. Nos.3,307,238, 3,844,004, 3,762,004, 3,464,097, 3,641,636, 4,309,800 and4,131,978, the contents of which are incorporated by reference herein.Thus, the needles that can be used in this invention may have barbconfigurations ranging from “non-aggressive” to “aggressive”. Thenon-aggressive barb configuration has a low degree of kick up, and so ischaracterized by a shallow barb gullet. This type of needle increasesloft and produces a low density product because there is relativelylittle mechanical interlocking. The aggressive barb configuration has ahigh degree of “kick up”, and is typically characterized by a deep barbgullet. Such needles increase consolidation and mechanical interlockingof the fibers.

The density of the batt also can be controlled by regulating the numberand relative weight of each web layer as it exits the carding operation.By varying the feed rate of the fibers into the carding operation, thetotal quantity of fiber in the web can be adjusted. For example, if thecrosslapping rate is held constant, and the web weight increases, thefinal batt density will be increased. Conversely, if the crosslappingrate is held constant and the web weight decreases, the final battdensity will decrease.

Heating

The batting is consolidated and bound by means of a heating process.This process serves to join at least some of the interstices betweenneighboring non-thermoplastic fibers. In this step the material isheated to a temperature at least equal to and preferably exceedingslightly the melting temperature of the thermoplastic component. Thematerial is held at this temperature for a period of time sufficient toallow at least some of the thermoplastic material to melt. Melting ofthe thermoplastic material results in the formation of globules ofthermoplastic material, and at least some of those globules collect atthe intersections and crossing points of the non-thermoplastic fibers.

It has been found that when the thermoplastic material includes PPSfibers, those fibers melt and take on a globular form, which causes somedensification of the resulting material. This can be seen in FIG. 7, aphotograph of m-aramid/PPS blended batting following heating. Typically,such increased densification can be on the order of 10-15% by volume.The sample shown in FIG. 7 was prepared using the procedures describedin the following paragraphs.

Production scale quantities of insulation have been produced using atenter frame dryer, measuring 280 cm wide and 30 meters in length (dryermanufactured by the Monsfort Company, St. Stefan, Austria). The materialwas prepared as described in Example 7 above, specifically, a blend of20% 1.2 denier 1.5″ staple length PPS fibers and 80% 2.0 denier 3.0″,staple length m-aramid fibers, formed into a thick lofty batting.Heating of the uncured batting was controlled as the batting passedthrough eleven separate heating zones, the first seven of which wereadjusted to maintain a temperature of 575° F.+/−10° F. The drive chainspeed was set at 1.5 meters per minute, and the unheated batting wasplaced on a supporting fabric attached to drive pins along the selvedgeand processed through the heating stage. The last four heating zoneswere adjusted to a temperature of 180° F. causing material to coolrapidly. This process cooled the material well below the glasstransition temperature of thermoplastic PPS to promote solidification inthe glassy or amorphous phase. The cooled thermoplastic material, whichcoalesced into globules, held the non-thermoplastic fibers together, andso served as a semi-elastic binder forming a structural lattice withinthe aramid fibers. The thermoplastic PPS binder, when used inconjunction with high modulus m-aramid structural fibers, results ininsulation having high resiliency, and other superior physicalproperties.

Heating also may be accomplished using other known methods that wouldtend to melt the thermoplastic fibers. One example of an alternativeheating method would be the use of radiant heaters. Such heaters can beplaced in close proximity to the top and bottom surface as the uncuredmaterial is passed between them on a metallic or fabric conveyor belt.Adjustment of the upper and lower heaters in conjunction with the beltspeed will allow uniform heating of the fabric.

Alternatively, other heating methods may involve the use of microwaveradiation, steam or similar methods to melt the thermoplastic binderfibers.

Finishing

In some situations, it may be desirable to provide insulation with adegree of water or oil repellency. This can be accomplished by applyinga finishing treatment to the insulation. Typically, such finishes aredispersed polymer emulsions that have been applied by immersing theinsulation in a water- or solvent-based emulsion bath. A padding processto remove excess treatment and a subsequent drying step immediatelyfollow. Production scale quantities of the low density m-aramidinsulating material were treated for oil and water repellence, followingthe procedure described above, using a PTFE(polytetrafluoroethylene)polymer emulsion provided by the du Pontcompany of Newark, Del.

Drying of the material was accomplished using the same tenter framedryer just described. This was done using a supporting fabric throughthe drying process. A temperature setting of 425° F.+/−10° F. was usedfor the entire drying process, and the drive chain speed was set to 2.0meters per minute.

Treatment finishes also could be applied using foam or spray to coat thematerial, and this would be followed by a drying step. The dryingtemperature should be sufficient to drive off excess moisture and orsolvent within the material, without damaging the material or theapplied finish.

Such finish coatings applied to the fiber mix after the cooling stepcould serve to render the resulting insulation less water absorbent,more fire-resistant, more soil resistant, more chemical resistant, moremildew resistant, more insect resistant and/or more radiation resistant.Multiple coatings, or coatings improving more than one of theseproperties, also could be applied.

If desired, the finish coating could include a material which develops afoam layer at an elevated temperature and, through oxidation, developsan ablative charring layer.

Other variations and modifications of this invention will be apparent tothose skilled in this art after careful study of this application. Thisinvention is not to be limited except as set forth in the followingclaims.

What I claim is:
 1. A method of manufacturing an insulating material,comprising the steps of: providing a plurality of fibers comprising anon-thermoplastic material; providing a thermoplastic material; mixingthe non-thermoplastic material and the thermoplastic material togetherto obtain a fiber mix; heating the fiber mix that that at least some ofthe thermoplastic material melts and form globules which at leastpartially surround and thereby link portions of said non-thermoplasticfibers; cooling the fiber mix so that the melted thermoplastic materialglobules form nodes which hold the non-thermoplastic fibers together;wherein said insulating material has a density of between approximately0.1 to 3.0 lbs/ft³.
 2. A method as in claim 1, wherein in the heatingstep the fiber mix is heated to a temperature of at least 538° F.
 3. Amethod as in claim 1, further comprising the step of consolidating thefiber mix.
 4. A method as in claim 3, wherein the consolidating stepcomprises a step of needling the fiber mix.
 5. A method as in claim 1,further comprising the step of attaching a fire blocking layer to theinsulating material.
 6. A method as in claim 1, wherein the fireblockinglayer includes at least one of polyacrylonitrile, ceramic, foil andpolymer film.
 7. A method as in claim 1, further comprising the step ofapplying a finish coating to the fiber mix after the cooling step.
 8. Amethod as in claim 7, wherein the finish coating renders the resultinginsulation at least one of less water absorbent, more fire-resistant,more soil resistant, more chemical resistant, more mildew resistant,more insect resistant and more radiation resistant.
 9. A method as inclaim 7, wherein the finish coating includes a material which develops afoam layer at an elevated temperature and, through oxidation, developsan ablative charring layer.
 10. A method as in claim 1, wherein thefibers of the non-thermoplastic material have a fineness of betweenapproximately 0.08 and 220 deniers.
 11. A method as in claim 1, whereinthe thermoplastic material comprises a plurality of fibers each having afineness of between approximately 0.08 and 220 deniers.